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| Titel |
Exchange pattern in the hyporheic zone of boreal rivers |
| VerfasserIn |
Brian Babak Mojarrad, Anders Wörman, Joakim Riml, Hjalmar Laudon |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142976
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| Publikation (Nr.) |
 EGU/EGU2017-6663.pdf |
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| Zusammenfassung |
| Rivers and groundwater are two essential components of hydrological systems which due to
their contrasting hydrochemical characteristics plays significantly different roles in
transporting water and solutes across the landscape. The interaction between these
two components takes place in the hyporheic zone, where the stream water and
groundwater mix in permeable sediments below the stream channel. This interaction is
driven by processes that occur on different temporal and spatial scales reflecting a
spectrum of landscape morphologies ranging from small stream features to large
geological structures. The water movement within the catchment is governed by
morphology due to its control on the groundwater head. Small scale and large scale
topographies cause dynamic and static head variation, respectively. Dynamic head is
controlled by the flow velocity whereas static head is regulated by variation in the water
surface elevation. Thus, hyporheic exchange models that include both small and
large scale topographies provide improved understanding of hyporheic exchange
properties.
Using COMSOL Multiphysics, the discharge patterns for both local hyporheic and
regional catchment-scale groundwater flow were derived for the Krycklan Catchment
(Sweden) with respect to the interacting circulation from a wide range of spatial scales in the
watershed including those of the stream-bed. The general methodology was to divide the
topography into three successive spatial scales: first the whole catchment was modeled in
order to obtain the large-scale groundwater flow field. Secondly, the groundwater
flow from the whole catchment was used as the boundary condition for a 1×1 km2
subdomain of the catchment. Finally, a 5×5 m2 region was used to represent the flow
along the stream and its adjacent hyporheic zone. Due to lack of observation of the
small scale topography of the stream bed a spectral approach was used to re-scale
the topography from the 100×100 m2 scale to the 5×5 m2 scale. By doing this
the flow field could be well represented down to decimeter scale and, thus, the
hyporheic exchange patterns could also be included. Utilization of the moderate and
large scale as the boundary condition for the small scale model output, allowed for
characterizing the size (depth) and fragmentation of the hyporheic zone caused by the
large-scale circulation of groundwater. The fragmentation of the hyporheic zone was
quantified from the simulation results in terms of spatial statistics of the vertical flow
velocity and expressed in terms of correlation length in semi-variance analyses. |
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